//============================================================================
//
//  This file is part of GPSTk, the GPS Toolkit.
//
//  The GPSTk is free software; you can redistribute it and/or modify
//  it under the terms of the GNU Lesser General Public License as published
//  by the Free Software Foundation; either version 3.0 of the License, or
//  any later version.
//
//  The GPSTk is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU Lesser General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public
//  License along with GPSTk; if not, write to the Free Software Foundation,
//  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110, USA
//
//  Copyright 2004, The University of Texas at Austin
//  Dagoberto Salazar - gAGE ( http://www.gage.es ). 2008, 2011
//
//============================================================================

//============================================================================
//
//This software developed by Applied Research Laboratories at the University of
//Texas at Austin, under contract to an agency or agencies within the U.S.
//Department of Defense. The U.S. Government retains all rights to use,
//duplicate, distribute, disclose, or release this software.
//
//Pursuant to DoD Directive 523024
//
// DISTRIBUTION STATEMENT A: This software has been approved for public
//                           release, distribution is unlimited.
//
//=============================================================================

/**
 * @file GravitationalDelay.hpp
 * This class computes the delay in the signal due to changes in gravity field.
 */

#ifndef GPSTK_GRAVITATIONALDELAY_HPP
#define GPSTK_GRAVITATIONALDELAY_HPP

#include <math.h>
#include "../gpstk/Position.hpp"
#include "../gpstk/ProcessingClass.hpp"



namespace gpstk
{

/** @addtogroup GPSsolutions */
//@{


/** This class computes the delay in the signal due to changes in the
 *  gravity field.
 *
 * This class is meant to be used with the GNSS data structures objects
 * found in "DataStructures" class.
 *
 * A typical way to use this class follows:
 *
 * @code
 *      // Input observation file stream
 *   RinexObsStream rin("ebre0300.02o");
 *
 *      // Load the precise ephemeris file
 *   SP3EphemerisStore sp3Eph;
 *   sp3Eph.loadFile("igs11513.sp3");

 *      // Reference position of receiver station
 *   Position nominalPos(4833520.2269, 41537.00768, 4147461.489);
 *
 *      // Object to compute gravitational delay effects
 *   GravitationalDelay grDelay(nominalPos);
 *
 *      // Some more code and definitions here...
 *
 *   gnssRinex gRin;  // GNSS data structure for fixed station data
 *
 *      // Set defaults of models. A typical C1-based modeling is used
 *   BasicModel model( nominalPos, sp3Eph);
 *
 *   while(rin >> gRin)
 *   {
 *
 *         // Apply the model on the GDS
 *      gRin >> model >> grDelay;
 *   }
 * @endcode
 *
 * The "GravitationalDelay" object will visit every satellite in the GNSS
 * data structure that is "gRin" and will compute the delay in the signal
 * caused by the change in the gravity field when the signal travels from
 * satellite to receiver.
 *
 * This effect is small, ranging from about 0.01 to 0.02 m, and it is only
 * used for precise positioning. The result is stored in the GDS with its
 * own type: "TypeID::gravDelay" (in meters) and should be used in the
 * prefit residual computation process, like the more general relativity
 * effect (which is related but it is not the same). Class
 * "LinearCombinations" takes it into account.
 *
 * \warning Be aware that this class DOES NEED both the receiver and
 * satellite position. The former is set with the common constructor or
 * the appropriate method, while you must use a class such a "BasicModel"
 * to compute the later and add it to the GDS.
 *
 * @sa BasicModel.hpp and LinearCombinations.hpp.
 *
 */
class GravitationalDelay : public ProcessingClass
{
public:

    /// Default constructor.
    GravitationalDelay() : nominalPos(0.0, 0.0, 0.0)
    { };


    /** Common constructor
     *
     * @param stapos    Nominal position of receiver station.
     */
    GravitationalDelay(const Position& stapos) : nominalPos(stapos)
    { };


    /** Returns a satTypeValueMap object, adding the new data generated
     *  when calling this object.
     *
     * @param epoch     Time of observations.
     * @param gData     Data object holding the data.
     */
    virtual satTypeValueMap& Process( const CommonTime& epoch,
                                      satTypeValueMap& gData )
    throw(ProcessingException);


    /** Returns a gnnsSatTypeValue object, adding the new data generated
     *  when calling this object.
     *
     * @param gData    Data object holding the data.
     */
    virtual gnssSatTypeValue& Process(gnssSatTypeValue& gData)
    throw(ProcessingException)
    {
        Process(gData.header.epoch, gData.body);
        return gData;
    };


    /** Returns a gnnsRinex object, adding the new data generated when
     *  calling this object.
     *
     * @param gData    Data object holding the data.
     */
    virtual gnssRinex& Process(gnssRinex& gData)
    throw(ProcessingException);


    /// Returns nominal position of receiver station.
    virtual Position getNominalPosition(void) const
    {
        return nominalPos;
    };


    /** Sets nominal position of receiver station.
     * @param stapos    Nominal position of receiver station.
     */
    virtual GravitationalDelay& setNominalPosition(const Position& stapos)
    {
        nominalPos = stapos;
        return (*this);
    };


    /// Returns a string identifying this object.
    virtual std::string getClassName(void) const;


    /// Destructor
    virtual ~GravitationalDelay() {};


private:


    /// Receiver position
    Position nominalPos;


}; // End of class 'GravitationalDelay'

//@}

}  // End of namespace gpstk

#endif   // GPSTK_GRAVITATIONALDELAY_HPP
